1. Field
Aspects of the present disclosure relate generally to wireless communication systems, and more particularly, to handovers in cellular wireless communication systems.
2. Background
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSDPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
As the demand for mobile broadband access continues to increase, research and development continue to advance the UMTS technologies not only to meet the growing demand for mobile broadband access, but to advance and enhance the user experience with mobile communications.
As an example, multi-point HSDPA has been recently introduced, in which multiple cells can provide high-speed downlinks within the same carrier frequency to a mobile station, such that the mobile station is capable of aggregating the transmissions from those cells. In some of these systems, an access terminal can include multiple MAC entities, each one configured to receive and process a respective one of the downlink transmissions. Here, because each MAC entity acts largely independently of the other MAC entities at the access terminal, certain issues can arise when the MAC entities deliver packets to higher layers. That is, the packets may be in the correct order as far as the MAC entity is concerned, but the combined order of packets coming from multiple MAC entities may be out of order. In particular, when a serving cell change occurs changing which cell is providing data to the respective MAC entities, certain issues can arise with the out-of-order packets at the higher layers, potentially causing a reset, e.g., at the RLC layer, when control packets are processed out of order.
Therefore, there is a desire in the field to improve the handling of packets by access terminals including multiple MAC entities to reduce potential issues caused by out-of-order packets.